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Structure Separation Experiments Phase 1 Preliminary Test Plan



Alexander Maranghides, Shonali Nazare, Eric Link, Kuldeep Prasad, Matthew Hoehler, Matthew Bundy, Steven Hawks, Frank Bigelow, William (Ruddy) Mell, Anthony Bova, Derek McNamara, Tom Milac, Daniel Gorham, Faraz Hedayati, Bob Raymer, Frank Frievalt, William Walton


The primary objective of this project is to assess structure-to-structure fire spread for structures located in the Wildland Urban Interface (WUI). Full-scale fire experiments will be conducted in which various types of structures (sources of fire) will be used to generate typical radiative and convective heat exposures on target structures (residential dwellings). The spacing between the source and target structures will be varied to identify safe structure separation distance (SSD). Most experiments will be conducted with construction materials currently listed in State of California building codes and using code compliant structural assemblies. A limited number of experiments will be conducted with enhanced, ignition resistant, materials that may not currently be listed by the State of California. The project is divided into three phases. Phase 1 will test sheds as fire sources, Phase 2 will test "in-law" buildings (small accommodation structures built close to primary residential structure) and Phase 3 will test single-family homes. Source terms from 1.39 m² to 24.8 m² (15 ft2 to 267 ft2) will be tested in Phase 1. Phase 2 will examine exposures from 40.87 m² (440 ft2) "in-law" buildings, and Phase 3 will characterize exposures from approximately 92.90 m² (1000 ft2) residences. Dimensions of Phase 3 single residences (source term) will be finalized after numerical modeling of the results from Phase 1 and Phase 2. This test plan focuses on Phase 1 research. Phase 1 aims to quantify the effects of shed sizes, construction types, fuel loading, and separation distance on the ignition of primary structures (residential dwellings). Experiments will be conducted at the National Institute of Standards and Technology (NIST) and the Insurance Institute for Business and Home Safety (IBHS). The NIST experiments will be conducted at the National Fire Research Laboratory (NFRL), and the IBHS experiments will be conducted just outside of the wind loading test cell. The opening of the test cell (13.7 m (45 ft) wide) will dictate the largest source structure that can be evaluated at IBHS.
Technical Note (NIST TN) - 2161
Report Number


Structure separation distance, fire, sheds, wind, heat release rate, mass loss, modeling, wildland-urban interface.


Maranghides, A. , Nazare, S. , Link, E. , Prasad, K. , Hoehler, M. , Bundy, M. , Hawks, S. , Bigelow, F. , Mell, W. , Bova, A. , McNamara, D. , Milac, T. , Gorham, D. , Hedayati, F. , Raymer, B. , Frievalt, F. and Walton, W. (2021), Structure Separation Experiments Phase 1 Preliminary Test Plan, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed April 18, 2024)
Created May 26, 2021, Updated November 29, 2022